A PET detector, as a key component of a PET device, mainly functions to acquire position, time and energy information of energy deposition for each γ photon in a PET event. To improve imaging performance of PET system, it is desirable that the adopted PET detector can provide Depth of Interaction (DOI) information, high detection efficiency, good time resolution and good spatial resolution in designing and implementing.
A conventional PET detector usually uses a single-layer scintillation crystal array or a single-layer continuous scintillation crystal as its scintillation crystal portion. For such a PET detector using a single-layer scintillation crystal array, the spatial resolution is determined by the size of the strip-type crystals in the scintillation crystal array. If a Silicon Photomultiplier (be abbreviated as SiPM) (or an Avalanche Photo Diode, hereafter APD) array is used as a photoelectric converter, the size of the strip-type crystal could not be too small, or else scintillating light output by several strip-type crystals will be received by a same SiPM (or APD) in a SiPM array (or an APD array), which finally leads to a result that the energy deposition position of γ photons could not be distinguished. For a PET detector using a single-layer continuous scintillation crystal, scintillating light which is caused by energy deposition of γ photons in the single-layer continuous scintillation crystal diffuses into a specific spatial distribution. The energy deposition position of the γ photons can be calculated based on the spatial distribution of the scintillating light detected by a photoelectric detector, but in order to accurately calculate the energy deposition position of the γ photons in the crystal and improve the spatial resolution of the detector, a large mount of reference data is needed to acquire critical system parameters (Joung, Jinhun; Miyaoka, R. S. Robert S.; Lewellen, T. K. Thomas K., “cMiCE: a high resolution animal PET using continuous LSO with a statistics based positioning scheme”, Nuclear instruments & methods in physics research, Section A, Accelerators, spectrometers, detectors and associated equipment, Volume: 489, pp. 584-598, 2002). The acquisition of the reference data is time-consuming and laborious, which determines that this kind of detector cannot be mass produced or be applied in a clinic PET system.
It is found promising to design a high performance PET detector by using a multilayer scintillation crystal. At present, the multilayer scintillation crystal is mainly adopted to acquire DOI information, and the scintillation crystal directly coupled to a photoelectric detector is always scintillation crystal array. Schmand M. et al design a PET detector with double-layers crystal array by using two types of scintillation crystals with different decay times, to acquire DOI information of energy deposition for γ photons in the PET detector (Schmand, M.; Eriksson, L.; Casey, M. E.; Andreaco, M. S.; Melcher, C.; Wienhard, K.; Flugge, G; Nutt, R., “Performance results of a new DOI detector block for a high resolution PET-LSO research tomography HRRT”, Nuclear Science, IEEE Transactions on, Volume:45, Issue:6, pp. 3000-3006, 1998). More energy deposition information of γ photons in the scintillation crystal can be acquired by designing a PET detector with a multilayer crystal.
Hence, to solve the technical problems in the conventional PET detector using a single-layer crystal, it is necessary to provide a multilayer scintillation crystal with novel structure to overcome shortcomings of the conventional PET detector.